The present invention relates to taps for mixing hot and cold water in sanitary facilities (wash-basins, showers, bathtubs, etc.), and in particular to a cartridge mixing valve provided with a thermostatic device suitable to maintain a constant water temperature.
It is known that conventional single-control mixing taps include a tap body with a cartridge mixing valve (hereinafter simply cartridge) removably inserted therein and a control lever for controlling a valve group, within the cartridge, made up of a pair of ceramic disks which adjust the flow of hot and cold water. This adjustment of the water, both in flow rate and in temperature, is carried out through the translation and rotation, respectively, of a mobile disk over an underlying fixed disk. In this way, the extent of aperture of the ports formed in said disks for the passage of hot and cold water is changed, and so is the ratio between hot water and cold water when they are mixed prior to the conveying to the tap mouth.
In order to maintain a constant temperature of the delivered water, both between two tap openings and during a same opening, it is possible to incorporate a thermostatic device in a conventional tap. Such a device acts downstream from the valve group by controlling the inflow of hot and cold water into the mixing chamber through respective ports. As it will be better explained further on, this control is carried out automatically by a thermosensitive bulb which causes the shifting of a slider suitable to change the aperture of said ports in the mixing chamber.
A first possible solution is to place the thermostatic device at the bottom of a common single-control mixer, i.e. below the valve group. This solution has several drawbacks both of installation, and of use and maintenance. First of all the assembly of the elements to be housed inside the tap body, the lower portion of the cartridge, is higher than in conventional cartridges, thus requiring a tap body which is higher than standard height. Secondly, the use of a single control for temperature and flow rate implies a difficult repeatability of temperature between two openings. Moreover, there is a poor precision in adjusting the temperature due to the limited travel of the single control, which generally has a maximum rotatory travel of 90.degree. around the tap mouth (.+-.45.degree.)
A third kind of drawback occurs when it is necessary to reach the thermostatic device for its maintenance. As a matter of fact, the most frequent need is to clean the mixing chamber from possible encrustations and/or deposits which may jeopardize the correct operation of the device. This need stems from the fact that the slider travel is of a few tenths of millimeter (usually max. 0,6 mm), therefore even small-size impurities may prove detrimental. However, the position of the thermostatic device requires the complete disassembly of the cartridge and therefore of the valve group too. This implies the necessity of cutting off the water, both hot and cold, upstream from the tap by means of a general valve or the like.
Another known solution suitable to overcome some of the above-mentioned drawbacks is to separate the flow rate control from the temperature control and to place the thermostatic device above the valve group. The use of two separate controls allows to achieve a more precise adjustment of temperature through the rotation of a ring along a greater arc (up to 360.degree.), and also without any problem of repeatability between two openings. Furthermore, the lower portion of the cartridge is small enough to be housed in a standard-size tap body. However, also this second solution is not free from drawbacks of installation, use and maintenance similar to the previous ones though to a lower degree.
First of all, the flow rate control is a horizontal rotating lever located above the ring for the temperature adjustment. This still implies a position of the flow rate control higher than in conventional taps, whereby even the use of a standard tap body results in a tap having a greater overall height. Moreover, the above-described arrangement makes it difficult to reach the ring for the temperature adjustment, since the user has to insert his hand between the tap mouth and the lever above.
Secondly, the thermostatic device is located between the flow rate control and the valve group controlled by the latter. As a result, the flow rate adjustment is necessarily transmitted by a connection which passes through the thermostatic device, which is possibly used directly as a transmission means. In any case, the more or less close coupling between the flow rate control and the temperature control leads to a mutual interference which may affect the device operation. In other words, when changing the flow rate it may happen that also the temperature is changed and vice versa. Moreover, the thermostatic device is stressed also by loads not depending on its specific operation.
Finally, the above-mentioned third kind of drawback is still present as far as the cleaning and maintenance of the thermostatic device are concerned. In fact, since the kinematic chain which transmits the flow rate adjustment has to be removed in order to reach the thermostatic device, it is still necessary to disassemble completely the cartridge and thus to cut off the water upstream from the tap.